Federal regulators are proposing new cars be required to have throttle override systems to prevent runaway acceleration in instances where the driver steps on the gas pedal and brake at the same time.

The National Highway Traffic Safety Administration said Thursday that it's proposing changing safety standards to require brake-throttle override systems in cars, trucks and buses weighing less than 10,000 pounds. The systems automatically brake while overriding the accelerator when both are pressed.

Many vehicles already come equipped with such systems.

The proposal is an outgrowth of investigations two years ago into claims that defects had caused unintended acceleration in some Toyota models. Government studies rejected those claims, but the probe uncovered several cases of drivers inadvertently pressing the brake and gas pedal at the same time.